1. Technical Field
The present invention relates generally to power producing devices and, more particularly, to a low-speed, low-pressure fluid-energy device that captures kinetic energy from the movement of fluid by the use of one or more reciprocating foils.
2. Description of Prior Art
Humans have long derived energy from flowing wind or water. The first great human machines were reciprocating air foils or what are commonly known as sailing ships. Water wheels and windmills represent some of the first machines deriving energy from non-animals sources. Hydro-power became a mature technology in the 1900s. Modern hydro-power has relied on high pressure/high head systems often associated with a dam or a reservoir. This technology has been limited to locations where there was a significant vertical drop for the water. These systems cause significant alteration of the landscape and the eco-system. These factors limit the potential growth of conventional hydro-power.
Wind power matured into a significant industry more recently. Modern wind power is mechanically different from hydro-power in that the moving fluid is low pressure and free flowing. The advancing technology of ever-larger turbines has made this economically viable but it is still limited to locations where there is sufficient average wind speed.
Low-pressure water power or hydrokinetic energy has been largely untapped. Many devices have been tested but they remain economically competitive only where the price of energy is extremely high. Hydrokinetic devices using tides and currents have more reliable and predictable sources of energy than wind power. The energy density of moving water is much higher than moving air, requiring smaller devices. The technology that turns slow moving water into commercial scale power generation will potentially tap one of the largest available sources of mechanical energy on the surface of the earth.
Fluid-energy machines operate by the same physical forces whether the fluid is a gas or liquid, high or low velocity, high or low pressure, high or low density. They incorporate some type of structure which is oriented at an angle of attack relative to the direction of flow of the fluid. Such structure may be a symmetrical foil, an asymmetrical foil, an airfoil, a hydrofoil, a turbine blade, a rotor, a sail, or the like. For simplicity and clarity, all such structures shall be denoted a “foil”. The foil has a leading edge and a trailing edge. The angle of attack is the angle formed between the chord line of the foil and the direction of flow of the fluid.
Energy transfer occurs either by drag when the foil and the fluid are moving in the same direction or by lift when the foil moves perpendicularly across the flow of moving fluid. Fluid-energy devices can be reciprocating or rotary. Most rotating machines have continuous power transfer while reciprocating machines can only transfer energy during part of their cycles.
A wind turbine or propeller has an axis of rotation that is collinear with the flow of the fluid. This provides great mechanical simplicity and continuous energy transfer. One important characteristic of this design is that the linear speed of any point on the blade is proportional to the distance from the axis. Commercial wind turbines have adapted to this relationship with large turbines using long contoured blades and high tips speeds (typically 6 to 7 times the wind speed) that remain efficient given sufficient wind speed.
In liquids the length of a rotating blade is limited by this blade speed relationship. Marine propulsion systems increase the width of the blade and its surface area in order to limit blade length. This results in significant turbulence and inefficiency.
To efficiently transfer energy from a slow moving fluid, a large slow moving foil is needed. A consistent relationship between the speed of the foil and the speed of the moving fluid minimizes turbulence and increases efficiency. This cannot be achieved with an axial turbine where blade speed varies by radius.
It is thus shown that there is a need for a device that can harness energy from a low pressure, low speed moving fluid.
It is therefore an objective of the present invention to provide a reciprocating fluid-energy device that can be used with any moving fluid.
It is a further objective of the present invention to provide a reciprocating fluid-energy device that extracts power from slow moving fluids.
It is yet a further objective of the present invention to provide a reciprocating fluid-energy device that extracts power from low pressure fluids.
It is yet a further objective of the present invention to provide a reciprocating fluid-energy device that is simple in design.
It is yet a further objective of the present invention to provide a reciprocating fluid-energy device that is efficient.
It is yet a further objective of the present invention to provide a reciprocating fluid-energy device that automatically and spontaneously reciprocates using only the force of the moving fluid.
It is yet a further objective of the present invention to provide a reciprocating fluid-energy device that is environmentally friendly.
Other features and attendant advantages of the present invention will become obvious to the reader and become fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings. It is intended that these objects and advantages are within the scope of the present invention. To the accomplishment of the above and related objects, this invention may be embodied in the form illustrated in the accompanying drawings. Attention being called to the fact, however, that the drawings are illustrative only, and that changes may be made in the specific construction illustrated and described within the scope of this application.